Electrochemical energy storage systems, such as batteries, supercapacitors and the like, have been widely proposed for large-scale energy storage applications. Various battery designs, including flow batteries, have been considered for this purpose. Compared to other types of electrochemical energy storage systems, flow batteries can be advantageous, particularly for large-scale applications, due to their ability to decouple the parameters of power density and energy density from one another.
Flow batteries generally include negative and positive active materials in corresponding electrolyte solutions, which are flowed separately across opposing sides of a membrane or separator in an electrochemical cell containing negative and positive electrodes. The flow battery is charged or discharged through electrochemical reactions of the active materials that occur inside the two half-cells. As used herein, the terms “active material,” “electroactive material,” “redox-active material” or variants thereof will synonymously refer to materials that undergo a change in oxidation state during operation of a flow battery or like electrochemical energy storage system (i.e., during charging or discharging). A full electrochemical cell contains two half-cells (i.e., a positive half-cell and a negative half-cell) that are separated by the separator material.
In order to increase the amount of energy that can be stored and released by a flow battery, a plurality of individual electrochemical cells can be placed in electrical communication with one another. Placing the individual electrochemical cells in electrical communication with one another typically involves positioning the individual electrochemical cells in a “cell stack” or “electrochemical stack” with a bipolar plate or similar material establishing electrical communication between adjacent electrochemical cells. Bipolar plates are electrically conductive but are substantially non-conductive toward fluid transport. Therefore, bipolar plates allow electrical communication to be established between adjacent electrochemical cells without exchanging electrolyte solutions therebetween.
Within an electrochemical cell, a bipolar plate can either serve directly as an electrode itself when placed in proximity to a separator or membrane, or the bipolar plate can abut a separate electrode material adjacent to the separator or membrane. Regardless of which configuration is present in a given electrochemical cell, it can be desirable to distribute an electrolyte solution efficiently to the separator to promote desired electrochemical reactions in close proximity to the separator. For example, inefficient distribution of an electrolyte solution can decrease operating efficiency and/or increase the occurrence of parasitic reactions at locations removed from the separator. As used herein, the term “parasitic reaction” will refer to any electrochemical side reaction differing from the desired oxidation-reduction cycle of the active material in an electrolyte solution.
Distribution of an electrolyte solution to the separator in an electrochemical cell can be accomplished using a bipolar plate. In some cases, designed flow fields can be incorporated in the bipolar plate to control the flow dynamics in a desired manner, as discussed in more detail hereinafter. Flow field architectures incorporating an open flow field, in which the flow dynamics of an electrolyte solution are largely non-regulated, are also possible. An unmodified porous carbon cloth or felt represents an illustrative material that can provide an open flow field in an electrochemical cell.
Designed flow fields that provide for directional change in at least one coordinate axis can often provide for more efficient cell operation than can open flow fields. Interdigitated flow fields, for example, can provide high current density values while maintaining the cell voltage at a desirable low level. Open flow fields require little, if any, special concerns during manufacturing of electrochemical cells. Designed flow fields, in contrast, can involve moulding and/or machining a plurality of flow channels in a conductive material. Definition of designed flow fields in this manner can add significantly to fabrication costs and represent a rate-limiting manufacturing step. Fabrication of interdigitated flow fields within a bipolar plate can be especially difficult to realize in a timely and cost-effective manner, particularly within a continuous production line.
In view of the foregoing, electrochemical cell configurations that can have designed flow fields readily incorporated therein and facile manufacturing thereof would be highly desirable in the art. The present disclosure satisfies the foregoing needs and provides related advantages as well.